Contract formally signed.Telstra has won a $1.6 billion contract to help build out and upgrade its hybrid-fibre coaxial (HFC) network for the NBN.

The deal comes on top of $11 billion definitive agreements already signed between Telstra and the national network builder, which were renegotiated in late 2014 to include Telstra's HFC network.

The telco today said that under the deal - expected to run until 2020 - Telstra would deliver all design, program management, construction management and scheduling activities within its HFC footprint across Sydney, Melbourne, Brisbane, the Gold Coast, Perth and Adelaide.

The bulk of field construction would be undertaken by NBN build partners, the telco said, while Telstra would deliver in-exchange construction activities and limited upstream in-field construction.

NBN and Telstra signed a memorandum of understanding for the contract late last year.

In the lead up to the formal signing, Telstra undertook some "early work" to prepare its exchanges and help with design and planning.

NBN is expected to announce a similar contract with Optus for its own HFC network, which the network builder similarly gained access to under the revised definitive agreements. Late last year it was revealed NBN was considering building over the Optus HFC network due to its degraded state.

Just hours after the telco and NBN announced a $1.6 billion deal for the rollout of Telstra's hybrid-fibre coaxial (HFC) network, the ACCC said it was worried the telco could potentially receive a competitive advantage from its various NBN contracts.

Among others, Telstra holds two contracts to fix faults on its copper network, and a four-year, $390 million contract to provide wider planning and design services for the NBN.

The new deal - which is in addition to the renegotiated $11 billion definitive agreements signed between Telstra and NBN in late 2014 to include the HFC network - will see Telstra help build and upgrade its HFC cable for the NBN.

It has been tasked with delivering all design, program management, construction management and scheduling activities within its HFC footprint across Sydney, Melbourne, Brisbane, the Gold Coast, Perth and Adelaide.

Under the deal, Telstra will deliver in-exchange construction activities and limited upstream in-field construction. Most field construction work will be undertaken by NBN build partners, the telco said.

While it recognised that Telstra's expertise would help roll out the NBN faster, the ACCC said the deal - and more broadly Telstra's involvement in the maintenance and construction of the NBN - posed competition problems.

“We have raised several concerns with Telstra and NBN Co, including that Telstra may receive a competitive advantage if it has access to better information than other service providers or if it is able to use infrastructure built for the NBN network before that infrastructure becomes available to other retail service providers,” ACCC chairman Rod Sims said in a statement.